The doctor blade is used in a toner cartridge assembly for ensuring a substantially even distribution of toner on a magnetic roller.
It has been observed that during the use of a toner cartridge assembly, the efficiency of the doctor blade decreases, whereby the quality of copying and or printing documents decreases.
This problem is especially important when toner cartridge assembly are reconditioned for use.
It has been proposed to apply on the doctor blade a strip comprising a polyurethane conductive layer and a polyester layer, the said strip having a total thickness of about 30-60 xcexcm. The polyester layer is glued on the doctor blade.
However, after 2,000-3,000 copies, the efficiency of such a doctor blade starts to decrease, whereby the quality of the following copies is poor. An adhesive conductive strip to be attached to a doctor blade of an electrostatic printing assembly is disclosed in U.S. Pat. No. 6,253,052.
The invention relates to a doctor blade with an improved efficiency, as well as a strip to be glued on a substrate of a doctor blade for improving its efficiency.
The invention relates to a doctor blade consisting of at least a substrate provided with an element having a face adapted for working with a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, said element being made at least partly of an elastic material. In the PCT application PCT/BE 00/00104, at least a part of the face adapted for working with a magnetic roller has an electrical surface resistivity of less than 1013 xcexa9 per square, preferably between 107 and 1012 xcexa9 per square, while at least a part of the element made at least partly of an elastic material has a thickness of at least 100 xcexcm, for example comprised between 100 xcexcm and 5 mm. Said face contacts the magnetic roller with interposition of toner particles. According to an example of said application, the layer contacting the developer roller has an abrasion resistance of less than 0.1 g.
It has now been discovered that an excellent working of the doctor blade seems more to be due to abrasion resistance and uniform density of the face contacting the developer roller, than due to the surface resistivity of said top face. When using a top coating applied directly on the substrate, said coating forms after drying or curing an uniform layer, i.e. a layer with uniform density or characteristics or properties at least at the top surface or contact surface (surface intended to contact the magnetic roller with interposition of toner particles).
When using a strip, it is of importance that the top face intended to contact the magnetic roller has uniform characteristics, such as uniform density, continuous outer elastic or elastomer film, together with good abrasion resistance, so as to obtain consistent triboelectric charge and consistent printing.
When using such a strip, it is advantageous to provide said strip with a coating having constant or uniform characteristics, said coating forming a continuous film or substantially continuous film. The coating is advantageously prepared from an elastomer material, for example from a dispersion containing polyurethane, such as an aqueous dispersion containing polyurethane. Tests made by attaching a polyurethane strip with a shore A hardness of 95 on a doctor blade, strip not provided with a coating for obtaining said continuous and uniform top face, have shown bad printing results. It seems that this bad printing is due to the absence of uniform density of the top face, whereby the abrasion of the top face due to the contact with the magnetic roller was not uniform, and varied form place to place. It shows therefore the importance to have an uniform and continuous top face or coating with good wear resistance for obtaining excellent printing for a long time.
The invention relates thus to a doctor blade comprising at least a flexible element with an outer face, a portion of said outer face being adapted for contacting with interposition of toner particles a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, in which said portion is provided with a coating (advantageously a flexible coating, such as an elastomer coating) or with a strip (advantageously a flexible strip, such as a flexible strip provided with a coating, preferably a flexible coating), said coating or strip having an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
The abrasion test ASTM-D4060 to which reference is made in the present specification is a taber abrader test (weight loss measurement), abrasion obtained after 1000 cycli with a load of 1,000 g, using an abrader wheel CS10.
The doctor blade comprises advantageously at least a flexible substrate provided with a flexible strip having a top face, a portion of which is adapted for contacting with interposition of toner particles a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, in which said portion is provided with a coating or strip having an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser. The top face is advantageously uniform or substantially uniform, i.e. has a uniform or substantially uniform top density.
According to an embodiment, the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) has a thickness (adhesive included) of at least 75 xcexcm (advantageously more than 100 xcexcm, for example comprised between 150 xcexcm and 5 mm, preferably between 200 xcexcm and 3 mm, most preferably between 200 xcexcm and 2 mm) measured at the level of the portion contacting the magnetic roller with interposition of toner particles.
For example, at least the portion of the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) contacting the magnetic roller with interposition of toner particles has a surface resistivity of more than 102 ohms per square.
In an advantageous embodiment, at least the portion of the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) contacting the magnetic roller with interposition of toner particles has a surface resistivity of more than 107 ohms per square, preferably more than 1.5 1012 ohms per square, most preferably more than 1013 ohms per square, such as 0.5 1014 and 1018 ohms per square.
The coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) is for example at least partly made of elastomer material, said material being advantageously selected among the group consisting of polyurethane, rubber, silicone, fluoropolymers or copolymers, polyacrylate, polymethacrylate, copolymer of acrylic and methacrylic acids, polyolefins, polypropylene, polyethylene, and mixtures thereof. In case the strip has to be conductive, conductive polymers or copolymers has to be used.
The substrate of the doctor blade is for example a substrate made at least partly of a material selected from the group consisting of polyurethane, silicone, polyester, metallic blade, PVC, polycarbonate, fluoropolymers or copolymers, polyacrylate, polymethacrylate, copolymer of acrylic and methacrylic acids, polyolefins, polypropylene, polyethylene, and mixtures thereof, said flexible strip being attached to said substrate
According to a detail of an embodiment, the flexible substrate has a free end edge, said free end edge being at least partly covered by said strip or flexible strip.
According to an advantageous detail, the strip or flexible strip is glued on the flexible substrate. For example a face of the strip is provided with a glue layer so as to facilitate the placement of the strip on the doctor blade.
According to another embodiment, the strip or flexible strip has a first portion covering at least a part of the substrate and a second portion forming an extension of the substrate from its free end edge.
According to a preferred embodiment, the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) has a Shore A hardness of less than 105, preferably less than 100, most preferably less than 96, possibly less than 94, for example less than 92. Strip with a Shore A hardness of more than 100, in some case of more than 96, are often considered as being too rigid.
According to advantageous details of embodiments of the invention, the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) has at least one characteristic (advantageously more than one, preferably all the following characteristics) selected in the group consisting of flexural modulus of 108 Pa or less (flexibility of the strip under tortional strain), a storage modulus of 108 Pa or less (i.e. a sufficient rigidity of the strip under tension), a Shore A hardness of less than 105, a Hoffman scratch-hardness test result of 2 or less (an abrasion resistance), and a color shift, in accordance with heat aging test ASTM D2244-79, within 1 delta E.
The methods of measurement of these characteristics are disclosed in U.S. Pat. No. 6,258,918 (Ho et al) having for subject matter a flexible polyurethane material, the content of said document is incorporated to this specification by reference.
The color shift is not an important parameter, as the polyurethane can be not transparent and can be discoloured due to aging, without modification of abrasion resistance.
Advantageously, the flexible substrate is provided with a longitudinal means for facilitating its bending in a direction with respect to the opposite direction. For example, the flexible substrate comprises a first portion adapted to be connected to a support, a second portion with a free end edge and adapted to contact the developer roller with interposition of the flexible strip, and an intermediate bending portion connecting the first and second portions. The strip can be attached to the substrate so as to cover partly the bending portion or so as to not cover the bending portion.
The thickness of the strip and the mechanical/physical properties of the top layer of the strip or coating (layer contacting the magnetic roller with interposition of toner particles) are advantageously selected so as to ensure the formation of a sufficient triboelectrical charges (electric charges formed due to the friction of the doctor blade on the magnetic roller), whereby ensuring that the toner particles are sufficiently charged by friction so as to ensure a correct transfer of toner particles on the magnetic roller and whereby ensuring good quality of printing.
According to a detail of a possible embodiment, the substrate has a free end edge and in that the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) is distant from said free edge of a distance comprised between 25 xcexcm and 2 mm.
The strip or flexible strip has advantageously a substantially rectangular shape with a variable thickness along its width. Preferably, the flexible strip has a first thickness along an edge adjacent to the free edge of the substrate and a second thickness for a portion distant from said edge, said second thickness being lower than the first thickness.
The strip is advantageously a rigid support or a semi rigid support or a flexible support, said support being provided with a coating having an abrasion resistance of less than 0.5 g. On the opposite face, the support is preferably provided with adhesive, such as a self adhesive layer.
The invention relates also to a toner assembly for a copier, printer or facsimile machine comprising at least:
a container for containing toner;
a magnetic roller, and
a doctor blade working with the magnetic roller,
the said toner assembly having the improvement that the doctor blade comprises at least a flexible element with an outer face, a portion of said outer face contacting with interposition of toner particles the magnetic roller, in which said portion is provided with a coating having an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser. Said coating contacting the magnetic roller with interposition of toner particles has advantageously one or more of the characteristics listed for the coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) applied on a doctor blade as disclosed here above in his specification. For example said portion has a flexural modulus of 108 Pa or less (flexibility of the strip under tortional strain) and/or a storage modulus of 108 Pa or less (i.e. a sufficient rigidity of the strip under tension) and/or a Shore A hardness of less than 94 and/or a Hoffman scratch-hardness test result of 2 or less (an abrasion resistance) and/or a color shift, in accordance with heat aging test ASTM D2244-79, within 1 delta E. The surface resistivity can vary for example from 102 to 1018 ohms per square, advantageously more than 107, preferably more than 1.5 1012, most preferably more than 1013 ohms per square.
The invention further relates to a toner assembly for a copier, printer or facsimile machine comprising at least:
a container for containing toner;
a magnetic roller, and
a doctor blade working with the magnetic roller,
the said toner assembly having the improvement that the doctor blade comprises at least a flexible substrate provided with a strip (preferably a flexible strip) having a top face, a portion of which is adapted for contacting with interposition of toner particles a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, in which said portion has an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
The doctor blade with the strip is advantageously a doctor blade of the invention as disclosed here above in this specification.
In a toner assembly of the invention, the doctor blade is not provided with electrical connecting means for connecting it to a voltage supplying means.
In the toner assembly of the invention using a coating or strip (advantageously flexible coating, flexible strip or strip provided with a flexible coating) attached to the substrate of the doctor blade, the doctor blade comprises at least a substrate having a free end edge and is provided with the coating or strip having a face contacting the magnetic roller with interposition of toner particles, and in which the coating or strip is distant from said free end edge of the substrate of a distance of at least 50 xcexcm.
The invention relates also to a process for printing or copying a document by means of a printer, copier or facsimile machine, in which at least:
toner is transferred on a magnetic roller;
a doctor blade contacts said magnetic roller with interposition of toner particles for distributing toner on the magnetic roller;
toner distributed by the doctor blade of the magnetic roller is transferred on a charge sensible element, and
toner transferred on the charge sensible element is transferred on a support, said process having the improvement that a doctor blade of the invention is used or that a toner cartridge of the invention is used.
For example, the doctor blade comprises:
at least a (possibly flexible) element with an outer face, a portion of said outer face being provided with a coating contacting with interposition of toner particles the magnetic roller, in which said coating has an abrasion resistance measured by the ASTM-4060 abrasion test of less than 0.5 g, preferably less than 0.2 g, most preferably less than 0.1 g, or
at least a flexible substrate provided with a strip or flexible strip having a top face, a portion of which is adapted for contacting with interposition of toner particles a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, in which said portion has an abrasion resistance measured by the ASTM-4060 abrasion test of less than 0.5 g, advantageously of less than 0.2 g, preferably less than 0.1 g.
Advantageously, the doctor blade is not provided with electrical connecting means for connecting it to a voltage supplying means.
The invention further relates to;
a process for reconditioning a doctor blade of a printer, copier or facsimile machine, said doctor blade having a flexible substrate, in which, prior to the gluing of a strip or flexible strip with a face having a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g (advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser) on the substrate of the doctor blade or prior the coating of the substrate of the doctor blade with a coating layer having (after drying or curing) a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g (advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser), the substrate having a shape distorted during a prior use thereof is submitted to a heat treatment and to a pressure for restoring substantially the shape of the substrate of the doctor blade before its use, and
a process for reconditioning a doctor blade of a printer, copier or facsimile machine, said doctor blade having a flexible substrate, in which, after gluing of a flexible strip with a face having a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g (advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser) on the substrate of the doctor blade or after the coating of the substrate of the doctor blade with a coating layer having (after drying or curing) a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g (advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser), the substrate having a shape distorted during a prior use thereof is submitted to a heat treatment and to a pressure for restoring substantially the shape of the substrate of the doctor blade before its use.
When applying a strip or flexible strip or coating on the substrate of the doctor blade, the substrate is preferably a substrate which has already been used, i.e. in which a longitudinal groove is formed at the contact line of the substrate with the developer roller.
The strip or flexible strip is advantageously glued on the flexible substrate of the doctor blade. Other fixing means of the flexible strip on the flexible substrate are possible, such as mechanical fixing means. In case of mechanical fixing means, the flexible strip is bound to a substantially rigid support (such as an aluminum plate), the longitudinal edges of which slides into rails of the substrate. In case of mechanical fixing means, the strip comprises advantageously a rigid or substantially rigid support provided with a coating with the requested abrasion resistance.
The face adapted for working with the magnetic roller has advantageously a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
Most preferably, not only the skin of the flexible strip or coating has good abrasion resistance, but even at least a part of the matrix or mass of the strip has such a good abrasion resistance. It means that even if the skin would be abraded, the layer just below the skin would still have a sufficient abrasion resistance.
According to another embodiment, the substrate is a flexible substrate having a face on which the strip or flexible strip or coating is attached, the said face of the substrate having a free end edge. The strip is distant from said free end edge advantageously of a distance of at least 50 xcexcm, preferably of at least 100 xcexcm, for example of 200 xcexcm to 600 xcexcm.
The strip, flexible strip, coating can be a multilayered strip, for example a strip comprising a top layer with a first surface resistivity (for example of more than 1.5 1012 ohms per square) and a base layer with another surface resistivity (said layer possibly containing conductive material and having for example a surface resistivity of less than 1012 ohms per square). Said top layer has for example a thickness of less than 50 xcexcm, for example comprised between 0.1 and 35 xcexcm (such as 0.5 xcexcm, 1 xcexcm, 3 xcexcm, 5 xcexcm, 10 xcexcm, 20 xcexcm, 25 xcexcm), while the base layer or layer have a total thickness advantageously sufficient for having a total thickness of the strip, flexible strip or coating of at least 100 xcexcm.
According to a preferred embodiment, the strip or coating is a mono layer strip or coating.
According to another possible embodiment, the doctor blade comprises a flexible substrate having a free end edge, at least one layer being glued on a face of the substrate at a distance from said free end edge so as to form a groove or recess with a depth of at least 100 xcexcm, preferably of at least 200 xcexcm. Said depth is advantageously comprised between 200 and 600 xcexcm. Said groove has advantageously a width of at least 200 xcexcm, for example comprised between 500 xcexcm and 5 mm, but preferably comprised between 500 xcexcm and 2 mm.
Although the doctor blade can be connected to a voltage supply means, the doctor blade is advantageously not connected to a voltage supply means or not intended to be connected to a voltage supply means (such as a DC power source). When the doctor blade is intended to be connected to a voltage supply means, the strip, flexible strip or coating of the invention can have a conductive layer intended to contact (with interposition of an adhesive layer) a conductive or semiconductive layer or support of the doctor blade.
The invention further relates to a strip for a doctor blade, i.e. a strip to be fixed on a doctor blade, preferably to be glued on the doctor blade, for example by means of hot melt glue. The means for attaching the strip on the substrate is a glue layer, an auto adhesive glue layer or a hot melt glue layer.
Preferably, the top face or layer adapted for working with a magnetic roller has an electrical surface resistivity of more than 1.5 1012 xcexa9 per square and a resistance against abrasion measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
According to a specific embodiment, prior to the gluing of the strip on the substrate of the doctor blade or prior to the coating of the substrate with an appropriate coating, the shape of said substrate being distorted during its use, the substrate is submitted to a heat treatment and to a pressure (advantageously with a bending) for restoring substantially the shape of the substrate of the doctor blade as before its use.
According to another possible embodiment, a strip is first glued on the substrate of the doctor blade, for example a polyurethane substrate or the substrate is first coated with an appropriate coating, said substrate having a shape distorted during its prior use. The substrate is thereafter submitted to a heat treatment and to a pressure (advantageously a bending) for restoring substantially the shape of the substrate of the doctor blade before its use.
Advantageously, the substrate is cleaned and/or dried before attaching a strip of the invention or before coating the substrate with the appropriate coating.
The top (conductive, advantageously not conductive) layer contains preferably at least polyurethane, in the form of a polymer or a copolymer or in the form of a mixture with another polymer or copolymer. The first layer is advantageously a thermoplastic layer.
The invention relates also to a doctor blade comprising at least a flexible substrate provided with a flexible strip having a top face, a portion of which is adapted for contacting with interposition of toner particles a magnetic roller of a machine selected from the group consisting of copier, printer and facsimile machine, in which said strip comprises a layer assembly with a first face adapted for contacting the magnetic roller and with a second face opposite to said first face, and a flexible element coated on its opposite faces with an adhesive, whereby one adhesive face of the element is attached to the second face of the layer assembly, while the other face of the element is attached to the flexible substrate by the adhesive. The use of a doable coated element or film or layer or substrate is advantageous for the manufacture of the strip to be attached on the doctor blade, and so as to be sure of the adhesion of the strip on the doctor blade. Delamination of the strip could also be prevented by using such a double coated element.
Advantageously, the flexible element is a film, whereby said film provided with adhesive on its both opposite faces has a thickness comprised between 20 xcexcm and 200 xcexcm, preferably between 50 and 150 xcexcm, most preferably about 100 xcexcm-125 xcexcm. The assembly layer can be a mono layered assembly or a multilayered assembly, said assembly being made of a flexible material, such as polyurethane, silicone, polyester, metallic blade, PVC, polycarbonate, fluoropolymers or copolymers, polyacrylate, polymethacrylate, copolymer of acrylic and methacrylic acids, polyolefins, polypropylene, polyethylene, and mixtures thereof.
The adhesive is advantageously an adhesive of the acrylic or methacrylic family.
Preferably, the first face of the layer assembly has an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
The strip of said doctor blade can further have one or more characteristics (such as thickness, surface resistivity, flexibility, storage characteristics, etc.) of the strip of any doctor blades as disclosed before in the present specification.
The invention further relates to a toner cartridge comprising at least a toner container, a magnetic roller, and a doctor blade, in which at least an element selected from the group consisting of the magnetic roller and the doctor blade is provided with at least a layer contacting the toner particles, said layer containing at least one or more lanthanides, salt thereof, lanthanide containing compound, lanthanide oxide, lanthanide hydroxide, etc. As lanthanide, Cerium (most preferably as cerium oxide) is preferred. The layer contains for example cerium oxide, possibly in admixture with one or more other lanthanide and/or with one or more electrically conductive compound, such as carbon particles, copper, silver, etc.
The magnetic roller and/or doctor blade are provided with a layer containing from 0.1% to 65% by weight, advantageously from 0.2 to 20% by weight, preferably from 0.5 to 10% by weight lanthanide or lanthanide containing compounds, preferably cerium (metal, salt, oxide, hydroxide, etc.).
The lanthanide containing layer is for example a layer of a strip adapted to be attached on the doctor blade, for example by means of adhesive, such as an adhesive layer or a glue layer or a hot-melt adhesive, or a layer of a coating applied on the doctor blade or portions thereof.
The lanthanide containing layer can be conductive, semi conductive or non conductive. For example the lanthanide containing layer can have a surface resistivity of more than 102 ohms per square, advantageously more than 106 ohms per square, preferably more than 1010 ohms per square, most preferably more than 1013 ohms per square, such as a surface resistivity comprised between 1014 and 1018 ohms per square.
The lanthanide containing layer can have a thickness comprised between 1 xcexcm and 10 mm, advantageously from 5 xcexcm up to 3 mm, preferably from 20 xcexcm up to 2 mm, such as 50 xcexcm, 100 xcexcm, 200 xcexcm and 500 xcexcm.
The lanthanide containing layer comprises for example lanthanide compounds or metal or mixtures thereof, as solid particles with a size lower than 100 xcexcm, advantageously lower than 25 xcexcm, preferably lower than 10 xcexcm, such as lower than 3 xcexcm, less than 2 xcexcm, less than 1 xcexcm or even lower (less than 0.5 xcexcm).
The lanthanide containing layer is for example made of a flexible or elastomer material, such as polyurethane, silicone, polyester, metallic blade, PVC, polycarbonate, fluoropolymers or copolymers, polyacrylate, polymethacrylate, copolymer of acrylic and methacrylic acids, polyolefins, polypropylene, polyethylene, epoxy, polyamide, and mixtures thereof.
The face of the layer adapted to contact the toner particles has advantageously an abrasion resistance measured by the ASTM-D4060 abrasion test of less than 0.5 g, advantageously less than 0.2 g, preferably less than 0.1 g, most preferably less than 0.01 g or even lesser.
The face of the layer adapted to contact the toner particles has also advantageously one or more characteristics selected among the group consisting of flexural modulus of 108 Pa or less (flexibility of the strip under tortional strain), a storage modulus of 108 Pa or less (i.e. a sufficient rigidity of the strip under tension), a Shore A hardness of less than 105, a Hoffman scratch-hardness test result of 2 or less (an abrasion resistance), and a color shift, in accordance with heat aging test ASTM D2244-79, within 1 delta E.
When using a strip to be attached on a substrate of a doctor blade, the strip is advantageously a multilayered strip.
The strip is for example a strip prepared in accordance to U.S. Pat. No. 5,089,330, the content of which is incorporated to said specification.
The invention relates also to the use of a toner cartridge with the magnetic roller and/or the doctor blade with a lanthanide containing layer in a printer, copier, fax, laser printer, etc. and a printing process using such a toner cartridge.
As typical lanthanide compounds, the following compounds given as examples only can be used:
Ce (metal), Pr (metal), Nd (metal), Pm (metal), mixtures of these metals, mischmetal, cerium oxide, cerium carbide, cerium hydroxide, cerium carbonate, neodium oxide, neodium carbide, praseodymium oxide, praseodymium carbide, praseodymium carbonate, and mixtures thereof.
These compounds, especially Cerium oxide particles with a size comprised between 0.1 xcexcm and 20 xcexcm, are abrasive and increase the triboelectric charge, whereby the life time of the doctor blade with a lanthanide containing layer and/or coating and/or strip is increased and whereby the transfer of toner particles on the magnetic roller is improved due to the increase of triboelectric charge by friction.